The present invention relates generally to systems and methods for measuring fluid levels, and more particularly to methods and structure for measuring oil level in a vehicle engine.
Accurately measuring fluid levels is important in many applications. As but one example, automatically monitoring the quality and amount of oil in a vehicle alerts drivers in a timely fashion when maintenance should be performed as dictated by the actual condition of the vehicle. Performing maintenance when it is actually required is preferred over following a predetermined, one-size-fits-all schedule that might be too long or too short for any given vehicle, depending on the way the vehicle is driven. If too long a period elapses between maintenance, a vehicle can be damaged. On the other hand, conducting maintenance when it is not needed is wasteful both in terms of labor and in terms of natural resources. For example, if a vehicle doesn""t require an oil change but nevertheless receives one, oil is in effect wasted.
Accordingly, systems have been provided for measuring various parameters of a vehicle""s engine oil, and to generate warning signals when maintenance is due as indicated by the condition of the oil. Among the parameters that are typically measured are oil temperature, condition, and level, and the signals from multiple sensors can be combined to generate the final engine oil maintenance signal. Of importance to the present invention is the accurate measurement of oil level.
As understood herein, oil level depends on many factors. Electrical properties of oil are used to measure level, which has the advantage of providing very accurate measurements. We have recognized, however, that the electrical properties depend on, among other things, temperature, oil brand, oil condition, oil contamination, making it difficult to accurately measure oil level over a wide temperature range and independently of brand and condition.
In conventional oil level sensors, a reference sensor is used along with a level sensor. The signal from the level sensor is divided by the signal from the reference sensor to cancel the effects of oil condition and so on, leaving a signal that represents level only.
Unfortunately, existing sensors have very small signal strengths, and, hence, poor signal-to-noise ratios. Significant amplification of the output signal is required, and this in turn introduces noise amplification and the problems attendant thereto. Moreover, to eliminate temperature differential effects the two sensors should be positioned close together. However, placing the sensors close together normally dictates using a relatively low input signal frequency that might not be effective at low oil temperatures. The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.
A fluid level sensor includes a receiver tube that is positionable in a container of fluid, such as a vehicle oil pan. The receiver tube defines an upright orientation when installed in the container, and a level tube is coaxially disposed in the receiver tube. Moreover, a reference tube is coaxially disposed in the receiver tube below the level tube relative to the upright orientation. As disclosed in detail below, a circuit is electrically connected to the tubes for outputting a signal representative of fluid level in the container.
In the preferred embodiment, each tube defines a respective interior communicating with the container, such that fluid in the pan can enter the interior of each tube. Each tube is made of metal, and the level tube and receiver tube together establish a first capacitor and the reference tube and receiver tube together establish a second capacitor. With this in mind, the above-mentioned circuit includes an output amplifier outputting a signal representative of voltage, as well as an input signal generator. The first capacitor interconnects the output amplifier and input signal generator. At least one switch selectively connects the second capacitor to ground.
In a particularly preferred embodiment, the circuit further includes at least one empty check capacitor connected to the switch. The switch is movable between a first position, wherein the second capacitor interconnects the output amplifier with the input signal generator and the empty check capacitor is connected to ground, and a second position, wherein the second capacitor is connected to ground and the empty check capacitor interconnects the output amplifier with the input signal generator. The input signal generator generates a sinusoidal wave, square wave, or triangle wave.
In another aspect, a method for measuring liquid level in a chamber includes providing a receiver tube and disposing a level tube in the receiver tube to establish a first capacitor. The method further includes disposing a reference tube in the receiver tube below the level tube to establish a second capacitor. The capacitors are connected to an electrical circuit having an input signal generator and an output. Using the circuit, the method envisions selectively connecting one of: the first capacitor, or second capacitor, to ground and then to the output, and outputting a signal representative of the level of liquid in the chamber.
In yet another aspect, an oil level sensor for a vehicle includes an oil pan, a receiver tube oriented upright in the oil pan, and a level tube in the receiver tube. The sensor also includes a reference tube in the receiver tube below the level tube.
In still another aspect, a fluid level sensor includes a reference plate positionable in a container of fluid. An upper plate is closely spaced from the reference plate, and a lower plate is also closely spaced from the reference plate below the upper plate. A circuit is electrically connected to the tubes for outputting a signal representative of fluid level in the container.